It depends on what is wrong with it. The fan usually sits on the motor's shaft pretty tightly so even if the nut or clip is removed, the fan will still be tight. Looseness is often caused by worn bearings in the motor. It is common for Chrysler to supply replacement assemblies rather than individual parts. That is done to insure the quality of the repair when it is done under warranty and they are paying the bill. It costs them more that way, but it takes the mechanic much less time so they make up their cost that way. The same is true when you are paying the bill. To install just the fan motor, which may be possible if it's available, will end up costing you a lot more for labor, and you have to worry that the original fan's mounting hole isn't stretched or wobbled out, and everything was assembled correctly. The complete assembly is a better value in the long run, and that's what your mechanic is after if he has your best interest at heart.